Semiconductor devices are becoming smaller and more dense with the evolution of new technology. However, increases in circuit density produce a corresponding increase in overall chip requirements to remain competitive. Chip manufacturers are therefore challenged to improve the quality of their products by identifying new ways of improving their manufacturing processes and material used to make their products. Whereas significant improvements have been made to eliminate or reduce process variability. Process improvements alone are not sufficient to improve both yield and reliability. Therefore, new processes and structures must be discovered in order for the semiconductor manufactures to remain competitive.
U.S. Pat. No. 4,020,987 (Hascoe) discloses a thick alloy core having upper and lower thin alloy coatings, which is punched to form a punched solder preform ring for use in hermetically sealing a container.
U.S. Pat. No. 5,159,432 (Ohkubo) discloses a package for a semiconductor device which uses an aluminum nitride (AlN) substrate, which has good heat radiating properties, and, which is sealed hermetically with low melting point glass.
U.S. Pat. No. 5,463,248 (Yano) teaches a semiconductor package comprising an aluminum nitride substrate having a semiconductor element mounted thereon, and a ceramic sealing member or cap secured thereto using a sealing glass and a fixing glass.
The above-mentioned processes all require furnace reflow of the entire package for hermetic sealing.
However, a resistance soldering process known as seam sealing can also be used to hermetically seal (solder/braze) metallic lids onto ceramic packages. These conventional alumina substrates, such as, based on ceramics or glass-ceramics packages, have relatively poor thermal conductivity, making it easy to do the localized heating required to reflow the solder/braze joint using the seam seal process.
However, aluminum nitride (AlN) substrates, by design have a relatively high thermal conductivity, making it extremely difficult to maintain sufficient localized heating to complete the wetting/reflow of braze/solder joint between a thermal cap or lid and the seal ring metallization on the AlN substrate.
The inventors however have discovered a way to overcome the problem of securing a thermal cap or lid to a relatively high thermal conductivity substrate, such as, for example, an AlN substrate, using an innovative seal ring thermal interposer between the thermal cap or lid and the AlN substrate, while accommodating the electronic devices mounted on the surface of the AlN substrate.